Indirect immunoprecipitation method has been used to purify mitochondrial mRNA fraction rich in 219K dalton poly(A)plus mRNA which codes for a 12.5K dalton polypeptide on in vitro translation. It is proposed to use extensive cDNA probe and hybridization with homologous and heterologous RNA fractions to achieve further purification. The purified mRNA will be used to prepare cDNA which can serve as a specific probe to localize the area on mitochondrial DNA coding for this mRNA. The cDNA probe will also be used to study the transcriptional patterns and mode of expression of mitchondrial genome.